(1) Field of the Invention
The present invention relates to an apparatus for capturing the energy of solar radiation.
(2) Description of Related Art including information disclosed under 37 CFR 1.97 and 1.98.
The physics of solar collectors and conversion of solar energy to electrical and mechanical power is well understood in the prior art. See, e.g., William Stine and Michael Geyer, Power From The Sun (2001) (chapters available online at www.powerfromthesun.net). Two major types of solar collection and energy conversion include methods in which (1) solar collectors concentrate sunlight to heat a heat transfer fluid to a high temperature and to generate steam that drives the power conversion system producing electricity (“thermal process”) and (2) photovoltaic cells are used to convert sunlight falling directly upon them to electricity (“photovoltaic process”). Stine and Geyer, Chapter 1.
The solar collector is a key element in a solar energy system. The function of a solar collector is to intercept the incoming solar radiation and change it into a useable form of energy that can be applied to meet a specific demand. Id.
Flat plate collectors are a commonly used type of solar collector. Id. Their construction and operation are simple. They also have the advantage of absorbing both energy coming directly from the disc of the sun and also diffuse and reflected energy coming from other directions. Id. Flat plate thermal collectors are seldom tracked to follow the sun's daily path across the sky. Id. However, it is common to see flat-plate photovoltaic panels mounted on mechanisms that track the sun about one tilted axis, thereby increasing the daily output of the panels.
When higher temperatures are required, concentrating solar collectors are used. Solar energy falling on a reflective surface (e.g., a mirror) is reflected onto a smaller area before it is converted to heat. The smaller surface can attain higher temperatures before heat loss due to radiation and convection wastes the collected energy. Most concentrating collectors can only concentrate the parallel radiation coming directly from the sun's disk and therefore must follow the sun's path across the sky. For prior art directed to sun tracking systems, see, e.g., Moeller, U.S. Pat. No. 4,223,174 (1980); Alsina, U.S. Pat. No. 6,642,691 (2003); Carroll et al., U.S. Pat. No. 6,886,339 (2005); Simon, U.S. Patent App. Pub. No. 2008/0029148 (2008); and McGlynn et al., U.S. Patent App. Pub. No. 2008/0029151 (2008).
The most important factor driving the solar energy design process is whether the energy it produces is economical.
In designing a solar collection system, the designer is interested in both the insolation or solar irradiance, a measure of the rate at which solar energy reaches a unit area at the earth, and also the irradiation or solar radiation, a measure of how much energy has fallen on a collector over a time interval. Insolation is usually measured in watts per square meter, while irradiation is usually measured in joules per square meter or watt-hours per square meter. Solar irradiance is simply the integration or summation of solar insolation over a time interval.
Solar energy from the sun is available all over the earth; however, the size of the collector needs to be increased to collect sufficient solar energy in regions in which the insolation may be relatively low. It is the primary task of the collection design to assure that the amount, quality and timing of the solar energy collected is appropriate to the user's needs. On the earth's surface there is both direct solar irradiance that comes directly from the disc of the sun and also diffuse irradiance that comes from all other directions, e.g., the downward scattering of solar irradiance as the sun's rays pass through the atmosphere and encounter nitrogen, oxygen, water molecules, water droplets and dust particles. Only flat plate, non-concentrating, collectors and some low-temperature types of concentrators can collect the diffuse component of solar radiation. Stine and Gayer, Ch. 2.
In the design of solar energy systems it is important to predict two angles: (1) the angle of incidence of the sun's rays, i.e., the angle between the sun's rays and a vector normal (perpendicular) to the aperture or surface of the collector and (2) the tracking angle, the amount of rotation required to align one of two axes of a collector normal to the sun's rays. These angles are important because the maximum amount of solar energy that could reach a collector is reduced by the cosine of the angle of incidence, and thus is at a maximum when the angle of incidence is normal or 90 degrees.
With two-axis tracking, the collector aperture will always be normal to the sun thus the angle of incidence will be 90 degrees. With one-axis tracking, the angle of incidence will be less than 90 degrees and will depend generally on the collector's position on the earth and the collector's orientation in space. Stine and Gayer, Ch. 3 and 4.
The prior art in published patents and patent applications is distinguishable from this invention in that:
U.S. Pat. No. 4,223,174 (Douglas E. Moeller, Sep. 16, 1980) discloses a sun-tracking solar energy conversion system. The instant invention is distinguishable at least in that its solar collectors are in a stepped configuration to allow the sun's rays to be collected on both the vertical and horizontal surfaces of the steps and it uses fold-out mirrors to expand the collection surface stuck by the sun's rays.
U.S. Pat. No. 5,576,533 (Wirojana Tantraporn, Nov. 19, 1996) discloses a circuit for converting solar energy into alternating current. The instant invention is distinguishable at least in that it also includes collectors in a stepped configuration with fold-out mirrors and a means for tracking the sun by pivoting about a horizontal axis.
U.S. Pat. No. 4,321,419 (Maurice C. Hanafin, Mar. 23, 1982) discloses a transparent protective cover for a solar panel. The instant invention is distinguishable in that it is not merely a protective cover.
U.S. Pat. No. 5,685,151 (Randy Ross, Nov. 11, 1997) discloses a method and apparatus for collecting, converting, storing and using solar energy, including salt (sodium chloride) as a heat storage medium. The instant invention is distinguishable at least in that it does not require the use of salt, does not use a reflective dish, and has its collectors in a stepped array with fold-out mirrors
U.S. Pat. No. 5,787,878 (George D. Ratliff, Jr., Aug. 4, 1998) discloses a solar concentrator including a steam boiler situated on a tower at the center of concentric tracks with mirrors focusing the sun's rays approximately on the boiler. The instant invention is distinguishable at least in that it has a semi-cylindrical configuration with collectors arrayed with straight steps and does not use mirrors to focus the sun's rays on a boiler.
U.S. Pat. No. 5,919,314 (II Song Kim, Jul. 6, 1999) discloses a sun tracking system based on the principle that power generated is inversely proportional to the angle between the sun and a normal to the surface of the collector and using a solar array for a satellite. The instant invention is distinguishable at least in that it does not use this method to track the sun and also in that it is designed to be used on the earth's surface.
U.S. Pat. No. 6,442,937 (Kenneth W. Stone et al., Sep. 3, 2002) discloses a solar power system that uses mirrors to concentrate solar rays on a single receiver and adjusts the surfaces of the mirrors to even out differences in the flow of energy over time. The instant invention is distinguishable at least in that its mirrors do not concentrate the sun's rays on a single receiver and it has a semi-cylindrical configuration with the solar collectors arrayed in straight steps.
U.S. Pat. No. 6,642,691 (Francesc Sureda Alsina, Nov. 4, 2003) discloses an autonomous interactive solar energy production system that can swivel on two axes to track the sun. The instant invention is distinguishable at least in that it has a semi-cylindrical configuration with the solar collectors arrayed in straight steps with fold-out mirrors.
U.S. Pat. No. 6,886,339 (Joseph P. Carroll et al., May 3, 2005) discloses a solar power collection system with parabolic-trough-shaped mirrors that focus the sun's rays along a focus line and that can rotate on one axis to track the sun. The instant invention is distinguishable at least in that its solar collectors are positioned in a stepped array and its fold-out mirrors do not focus the sun's rays along a focus line.
U.S. Pat. No. 6,930,237 (Gilberto Mattiuzzo, Aug. 16, 2005) discloses a device for converting solar radiation into electric power in which solar panels are retained on multiple supporting arms that protrude from a vertically elongated body. The instant invention is distinguishable at least in that it does not require a vertically elongated body, has a means for tracking the sun and has its collectors arrayed in straight steps with fold-out mirrors.
U.S. Patent Application No. 2008/0029149 (Daniel Simon, Feb. 7, 2008) discloses an apparatus in which solar cells and reflectors are in a stepped array. The instant invention is distinguishable at least in that it has a semi-cylindrical main body which can pivot to track the sun and has collectors in a stepped array with fold-out mirrors allowing the reflected rays to strike the collectors on both the horizontal and vertical steps.
U.S. Patent Application No. 2008/0029151 (Daniel McGlynn et al., Feb. 7, 2008) discloses a solar power system including semiconductor solar cells, trough-shaped or Cassegrain reflectors, a solar tracker, and a heat spreader for cooling the solar cells. The instant invention is distinguishable at least in it has a semi-cylindrical main body with solar collectors in a stepped array with fold-out mirrors.
Japanese Patent No. 2007-150220 (K. Matsura, Jun. 14, 2007) discloses a sunlight reflective apparatus for solar electric power generation having a concave mirror that concentrates sunlight on a solar cell module. The instant invention is distinguishable in that it has a semi-cylindrical main body with solar collectors in a stepped array.